EDEN PRAIRIE, Minn. -- Vikings wide receiver Percy Harvin is back with the team after an overnight hospital stay following a scary migraine attack, though his return to the field remains unclear.

Harvin was on the practice field Friday morning, wearing a T-shirt, shorts and tennis shoes, drinking Gatorade while smiling and chatting with coaches. He exchanged handshakes and hugs with a few teammates -- waving at Pat Williams after the defensive tackle yelled "Hey, Perce, what's up?" -- before walking inside the Vikings' practice facility.

Harvin has missed all but a handful of practices since training camp began three weeks ago, plagued again by the unpredictable, debilitating migraine episodes that can leave him unable to function, let alone put on a helmet and pads and run around the field.

But Harvin was, by all accounts, doing fine one day later.

"He probably could've come over here and done some things today, except for the fact that they've got a couple tests that they want to finish with," Vikings coach Brad Childress said. "I don't know that we're going to solve that riddle immediately, and I don't know that there's any quick fixes. I think it's just going to be a work in progress, and even though you'd like to stick it in a box and have it be fixed this way. History has told migraines aren't that way."

Harvin will not travel with the team to San Francisco for Sunday's preseason game against the 49ers.

With the regular-season opener in New Orleans less than three weeks away, Harvin's availability -- let alone ability to contribute at an elite level -- is in question.

Childress downplayed the concern.

"He had a few (migraines) last year that he dealt with and we dealt with, and if it was his first choice, he'd be here for all the prep for every week," Childress said. "But the fact is he has played well in games that he's had a migraine the week of the game, and it just matters whether it's a short one, a hard one, a two-day one and then what he was able to get out of the game plan."

Wide receiver Sidney Rice, who hasn't practiced yet because of a lingering hip injury, also is in that uncertain category. Rice said Friday that he's having "a little bit of pain" and acknowledged his readiness "is still up in the air" for the big season opener against the Saints on Sept. 9.